APPARATUS FOR PULSE WIDTH MODULATION AND METHOD FOR CONTROLLING THEREOF
An apparatus for generating a pulse width modulated (PWM) signal to control a transforming circuit to drive a loading is provided. The apparatus includes an error signal generator, a control circuit and a comparator. The error signal generator includes a first input terminal for receiving a reference voltage, a second input terminal for receiving a feedback signal generated based on an operating state of the loading respectively, and an output terminal for outputting an error status signal. The comparator includes a first input terminal for receiving the error status signal, a second input terminal for receiving a compare signal, and an output terminal for generating the PWM signal. The control circuit determines whether to provide a setting signal coupled to the output terminal of the error signal generator based on at least one control signal.
Latest BEYOND INNOVATION TECHNOLOGY CO., LTD. Patents:
- Boost apparatus with integration of OCP detection and OVP detection
- Boost apparatus with over-current and over-voltage protection functions
- Load driving apparatus relating to light-emitting-diodes
- Successive approximation register analog-to-digital converter
- Light emitting diode driving apparatus capable of detecting whether current leakage phenomenon occurs on LED load and light emitting diode driving method thereof
This application claims the priority benefit of Taiwan application serial no. 95133411, filed on Sep. 11, 2006. All disclosure of the Taiwan application is incorporated herein by reference.
BACKGROUND OF THE INVENTION1. Field of the Invention
The present invention relates to an apparatus for pulse width modulation (PWM) and a method for controlling the same, and more particularly, to a circuit and a control method capable of lowering the transient period of a PWM apparatus.
2. Description of Related Art
Pulse width modulation (PWM) is a common and a practical control method. Many types of control devices use PWM to drive a loading. For example, in a cold cathode fluorescent lamp (or a light-emitting diode) module, PWM techniques are deployed to control the brightness of the cold cathode fluorescent lamp (or the light-emitting diode).
The conventional PWM apparatus 100 includes an error amplifier 102, a comparator 104, a signal generator 106 and a driving circuit 108. The positive input terminal of the error amplifier 102 receives a reference voltage Vref. The negative input terminal of the error amplifier 102 receives the feedback signal Sf and is coupled to the output terminal of the error amplifier 102 through a compensating capacitor C1. In addition, the negative input terminal of the comparator 104 is coupled to the signal generator 106, and the positive input terminal of the comparator 104 is coupled to the output terminal of the error amplifier 102. The output from the output terminal of the comparator 104 is transmitted to the driving circuit 108.
As shown in
As shown in
Moreover, in the process of dimming the cold cathode fluorescent lamp, the increase in the pulse width of the pulse width modulated signal Sp may lead to an increase in the lamp voltage VLamp until the lamp is ignited. After the lamp conducts and normal operating voltage is reached for a period of time, the lamp current ILamp will reach 90% of the predetermined current value. However, due to the characteristic of the lamp as shown in
Accordingly, the present invention is to provide a pulse width modulated (PWM) apparatus having a shorter transient period so that the PWM apparatus can be applied to a high speed loading system with the possibility of extending the life span of the loading.
The present invention is also to provide a control circuit and a method for controlling a PWM apparatus to generate a pulse width modulated signal to drive a loading and simultaneously decrease the transient period of the PWM apparatus.
The present invention provides a pulse width modulated (PWM) apparatus for generating a pulse width modulated signal to control a transforming circuit to drive a loading. The apparatus includes an error signal generator, a control circuit and a comparator. The error signal generator includes a first input terminal for receiving a reference voltage, a second input terminal for receiving a feedback signal generated based on an operating state of the loading respectively, and a first output terminal for outputting an error state signal. The comparator includes a third input terminal for receiving the error state signal, a fourth input terminal for receiving a compare signal, and an second output terminal for generating the PWM signal. The control circuit determines whether to provide a setting signal coupled to the first output terminal of the error signal generator based on at least one control signal.
According to another aspect of the present invention, a control circuit suitable for controlling a PWM apparatus is provided. The PWM apparatus includes an error signal generator and a feedback compensation unit. A first input terminal of the error signal generator is coupled to a first reference voltage, a second input terminal is coupled to a feedback signal and an output terminal outputs an error state signal. The feedback compensation unit is coupled between the second input terminal and the output terminal of the error signal generator. The control circuit includes a signal generator coupled to one end of the feedback compensation unit for generating a signal for adjusting the voltage across the feedback compensation unit.
According to another aspect of the present invention, a method for controlling pulse width modulation (PWM) suitable for controlling a PWM apparatus to generate a pulse width modulated signal to control a transforming circuit to drive a loading is provided. The control method in the present invention includes the following steps. First, the state of the PWM apparatus is detected to determine whether or not it is in a specified state or not. When the PWM apparatus is in the specified state, one of the error state signals of the PWM apparatus is set to a predetermined value.
Because the present invention is able to determine whether to set the level of the error state signal to a predetermined value according to the operating state of the PWM apparatus, the transient period of the PWM apparatus can be effectively reduced.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.
The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.
Reference will now be made in detail to the present preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings and the description to refer to the same or like parts.
The present invention adjusts the level of the error state signal Se1 through a signal so that the level at the beginning of the operation is already at an appropriate level, thereby shortening time lag between T1 and T2. As shown in
In addition, a positive input terminal of the comparator 304 receives an error state signal Se2 output from the error signal generator 302, a negative input terminal of the comparator 304 receives a compare signal Sc, and an output terminal of the comparator 304 is coupled to the driving circuit 306. In the present embodiment, the compare signal Sc can be a triangular wave signal or a saw-tooth wave signal from a signal generator 309.
Also, as shown in
More specifically, the PWM apparatus 300 in the present embodiment includes a control circuit 308 used for determining whether to adjust the level of the error state signal Se2 according to at least one control signal, and preferably setting the level of the error state signal Se2 to a predetermined value. In the present embodiment, the predetermined value is a predetermined voltage greater than 0 so that the transient period of the PWM apparatus 300 can be reduced.
For example, in the burst dimming process of the conventional technique, the burst-dimming signal will be transmitted to the negative input terminal of the error signal generator 302. When the burst-dimming signal is at a high voltage level, the transmission of energy to the loading is stopped. Conversely, when the burst-dimming signal is at a low voltage level, the transmission of energy to the loading is resumed. When the burst-dimming signal is at a high voltage level (for example, 3.3 V), the voltage level at the negative input terminal of the error signal generator 302 is pulled up (assuming up to 2.0V) so that the error state signal Se2 from the output of the error signal generator 302 is zero and the voltage across the feedback compensation unit 301 is 2.0V. When the burst-dimming signal is changed to a low voltage of 0V, the feedback signal Sf is also at 0V so that the voltage level at the negative input terminal of the error signal generator 302 is 0V (here, the ground is assumed to be 0V, the same in the following embodiments), and the voltage of the error state signal Se2 at the output terminal of the error signal generator 302 is −2V due to the voltage across the feedback compensation unit 301. Hence, the transient period from −2V to the voltage level VL (assuming to be 0.5V) of the compare signal Sc is relatively long. In the present invention, the error state signal Se2 at the output terminal of the error signal generator 302 is set to 2.4V when the burst-dimming signal is at a high voltage level, so that there is a voltage of −0.4V across the feedback compensation unit 301. Therefore, when the burst-dimming signal is changed to a low voltage of 0V, the error state signal Se2 at the output terminal of the error signal generator 302 is 0.4V. Obviously, for a condition that the voltage level at the negative input terminal of the error signal generator 302 is pulled to the reference voltage Vref, the voltage across the feedback compensation unit 301 can be set in the neighborhood of (VL-Vref). Using Vref=1.0V as an example, when the burst-dimming signal is changed to a high voltage level, the error state signal Se2 can be set to 1.4V so that the voltage across the feedback compensation unit 301 is −0.6V (in the neighborhood of 0.5V-1.0V). Therefore, when the burst-dimming signal is changed to a low voltage level, the voltage level at the negative input terminal of the error signal generator 302 can rapidly reach 1V while the error state signal Se2 begins from 0.4V. For a dimming method that does not send the burst-dimming signal to the negative input terminal of the error signal generator (for example: in the following embodiment, a dimming signal serves as the enable signal EA to enable the PWM apparatus 300, so that when the burst-dimming signal is at a ‘low’ voltage level, the transmission of energy to the loading is stopped, and when the burst-dimming signal is at a ‘high’ voltage level, the transmission of energy to the loading is resumed), person having ordinary skill in the art may deduce on their own the required predetermined value of the voltage across the feedback compensation unit 301. Thus, a detailed description is omitted.
When the voltage level at the output terminal of the error signal generator 302 is set by the control circuit 308 to be the predetermined voltage value, the voltage at the other terminal of the capacitor C2 will not change instantaneously due to voltage continuities in capacitors. To prevent the occurrence of false actions, the control circuit 502, which is able to work synchronously with the control circuit 308, is disposed in the circuit shown in
In the present embodiment, the switch 601 may include an NMOS transistor 602. The first source/drain terminal and the second source/drain terminal of the NMOS transistor 602 are coupled to the first and the second terminal of the switch 601 respectively, and the gate of the NMOS transistor 602 is coupled to the control terminal of the switch 601. Furthermore, the switch 603 may be implemented using a PMOS transistor 604. The first source/drain terminal and the second source/drain terminal of the PMOS transistor 604 are coupled to the first and the second terminal of the switch 603 respectively, and the gate of the PMOS transistor 604 is coupled to the control terminal of the switch 603.
The foregoing description has disclosed the circuit structure of the control circuit 308, and the control circuit 502 in
When the switching signal X is at a low voltage level, the switching signal X′ is at a high voltage level so that both transistors 602 and 604 simultaneously conduct. Thus, the resistors R1 and R2 together form a voltage divider circuit and output a voltage signal at the output terminal K1. Therefore, by adjusting the values of the resistors R1 and R2, the level of the error state signal Se2 in
In the present embodiment, the enable control signal EA is used for determining whether to enable the PWM apparatus 300 (as shown in
As shown in
When the enable control signal EA changes from ‘1’ to ‘0’, the PWM apparatus 300 shut down. If the PWM apparatus only temporarily shut down, the power of the supply system will be maintained above the working voltage level so that the working voltage detection signal is ‘1’ and the output from the exclusive NOR gate 702 is ‘0’. Those skilled in the art would understand that the output from the AND gate 704 is ‘0’. In other words, the switching signal X is ‘0’ and the switching signal X′ is ‘1’ so that both the transistors 602 and 604 conduct. Then, the control circuit 308 forces the level of the error state signal Se2 to the predetermined value. Any output from the PWM apparatus 300 is immediately stopped so that an instantaneous shutdown is achieved. On the other hand, when the PWM apparatus 300 only temporarily shuts down, the level of the error state signal Se2 (as shown in
When the operation of the PWM apparatus 300 of the present invention is in error, the error detection signal ERR is ‘1’, and is ‘0’ after an inversion. Therefore, the output from the AND gate 704 is ‘0’ so that the switching signal X is ‘0’ and the switching signal X′ is ‘1’, and both transistors 602 and 604 conduct. Consequently, when the PWM apparatus detects that the loading operates abnormally, the control circuit 308 is able to set the level of the error state signal Se2 to below the lowest level (as shown in
In some embodiments, when the loading is a light source module, for example, a light-emitting diode module, the enable signal EA can also serve as a dimming signal for dimming the loading.
As shown in
As shown in
In some other embodiments, the enable control signal EA and the dimming signal are not the same signal. Therefore,
The AND gate 902 receives the working voltage detection signal HV and the enable control signal EA, and generates an output signal accordingly to the exclusive NOR gate 702. The reception of the dimming signal DIM by the AND gate 902 can also be judged by using the steps as shown in
A full description on the operation of the rest of the logic gates in the embodiment shown in
As shown in
When the state of the PWM apparatus 300 is a specified state, step S11 is executed to set an error state signal of the PWM apparatus 300 to a predetermined value, preferably greater than 0V. Conversely, if the state of the PWM apparatus 300 is not a specified state, step S12 is executed to generate an error state signal according to the operating state of the loading.
Next, in step S13, the error state signal is compared with a compare signal to generate a pulse width modulated signal to drive the loading. The compare signal includes a first level and a second level, wherein the first level is higher than the second level and the second level is higher than the predetermined value. Moreover, in the present embodiment, when the state of the PWM apparatus 300 is not a specified state, the error state signal is generated through comparing a working voltage signal from the loading with a reference voltage.
Because the present invention is capable of setting the level of the error state signal to the predetermined voltage level when the PWM apparatus is in some specified states, the transient period of the PWM apparatus is effectively reduced.
Furthermore, as mentioned before, for some of the loadings (for example, a fluorescent lamp) having a slow enabling period or a slow generating of the feedback signal. In such cases, beside setting the feedback compensation unit 301 based on the 0V voltage level at the negative input terminal of the error signal generator 302, the signals received by the control circuit 308 (for example, the enable control signal EA, the working voltage detection signal HV, the error detection signal ERR, the dimming signal DIM and so on) may be processed with a time delay (a predetermined time delay). Alternatively, the operation of the control circuit 308 is stopped when the feedback signal Sf (or the voltage level at the output terminal of the error signal generator 302) is greater than a predetermined value. As a result, the control circuit 308 is able to accelerate the stabilization of the voltage level at the output terminal of the error signal generator 302 and reduce the transient period of the pulse width modulated signal Sp from its initiation to its stabilization. In other words, after the pulse width modulated signal Sp is generated, the control circuit in the present invention provides an auxiliary signal. Consequently, the feedback compensation unit 301, besides the current generated by the error signal generator 302, also simultaneously receives an auxiliary signal provided by the control circuit 308 to accelerate the adjustment of the voltage across the feedback compensation unit 301 to a stable state. The auxiliary signal can be a voltage signal or a current signal.
When the auxiliary signal is a voltage signal, the level of the auxiliary signal is preferably higher than the level VL of the compare signal Sc in order to reduce the required transient period of the pulse width modulated signal Sp from its initiation to its stabilization. As shown in
Obviously, the control circuit 1208 for providing the auxiliary signal may exist independently and there is no need to coexist inside the control circuit 308 (and the control circuit 502).
Through the embodiments shown in
It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention cover modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.
Claims
1. A pulse width modulation (PWM) apparatus for generating a pulse width modulated signal to control a transforming circuit to drive a loading, the pulse width modulation apparatus comprising:
- an error signal generator, having a first input terminal, a second input terminal and a first output terminal, wherein the first input terminal and the second input terminal are coupled to a first reference voltage and a feedback signal generated based on an operating state of the loading respectively, and the first output terminal outputs an error state signal;
- a first comparator, having a third input terminal, a fourth input terminal and a second output terminal, wherein the third input terminal receives the error state signal, the fourth input terminal receives a compare signal, and the second output terminal outputs the pulse width modulated signal; and
- a first control circuit, for providing a first setting signal coupling to the first output terminal of the error signal generator based on at least one control signal.
2. The PWM apparatus of claim 1, wherein the compare signal is a triangular wave or a saw-tooth wave and the level of the first setting signal is substantially equal to or below a trough level of the compare signal.
3. The PWM apparatus of claim 1, further comprising a feedback compensation unit, having one terminal coupled to the second input terminal of the error signal generator and another terminal coupled to the first output terminal of the error signal generator.
4. The PWM apparatus of claim 3, wherein the level of the first setting signal is determined based on at least one of the level of the compare signal and the first reference voltage.
5. The PWM apparatus of claim 4, wherein the first setting signal is for adjusting a voltage across the feedback compensation unit
6. The PWM apparatus of claim 1, wherein the first control circuit comprises a first switching control unit for controlling whether or not to output the first setting signal.
7. The PWM apparatus of claim 6, wherein the first control circuit comprises:
- a first switch, for determining whether or not to couple the first output terminal of the error signal generator to ground according to a first switching signal generated by the first switching control unit; and
- a second switch, for determining whether or not to couple the first output terminal of the error signal generator to a voltage source according to a second switching signal generated by the first switching control unit.
8. The PWM apparatus of claim 7, wherein the first switch is an NMOS transistor with a first source/drain terminal grounded, a second source/drain terminal coupled to the first output terminal of the error signal generator through a first resistor and a gate terminal coupled to the first switching signal, and the second switch is a PMOS transistor with a first source/drain terminal coupled to the first output terminal of the error signal generator through a second resistor, a second source/drain terminal coupled to the voltage source and a gate terminal coupled to the second switching signal.
9. The PWM apparatus of claim 1, wherein the least one control signal comprises an enable control signal, a working voltage detection signal, an error detection signal, a dimming signal, the feedback signal or the error state signal.
10. The PWM apparatus of claim 9, wherein the first control circuit continuously provides the first setting signal for a period after the dimming signal represents to resume a transmission of energy to the loading wherein the period is determined based on the level of the least one control signal.
11. The PWM apparatus of claim 1, further comprising a second control circuit for providing a second setting signal coupled to the second input terminal of the error signal generator based on at least one control signal.
12. The PWM apparatus of claim 11, wherein the second control circuit comprises a second switching control unit for controlling whether or not to output the second setting signal.
13. The PWM apparatus of claim 12, wherein the second control circuit further comprises:
- a third switch, for determining whether or not to couple the second input terminal of the error signal generator to ground according to a third switching signal generated by the second switching control unit; and
- a fourth switch, for determining whether or not to couple the second input terminal of the error signal generator to a voltage source according to a fourth switching signal generated by the second switching control unit.
14. The PWM apparatus of claim 11, wherein the level of the second setting signal is substantially equal to or above the level of the first reference voltage.
15. The PWM apparatus of claim 1, further comprising a third control circuit for providing an auxiliary signal coupled to the first output terminal of the error signal generator based on at least one control signal.
16. The PWM apparatus of the claim 15, wherein at least one of the control signals comprises a dimming signal, the feedback signal, or the error state signal.
17. The PWM apparatus of claim 16, wherein the third control circuit comprises a current source and a switching control unit, and the switching control unit is used for determining whether or not the current source provides a current signal as the auxiliary signal based on at least one control signal.
18. The PWM apparatus of claim 16, wherein the third control circuit comprises a voltage source, a switch and a switching control unit, the voltage source is coupled to the first output terminal of the error signal generator via the switch, and the switching control unit controls the switch so as to determine whether the voltage source provides a voltage signal as the auxiliary signal based on at least one control signal.
19. The PWM apparatus of claim 16, wherein the third control circuit comprises:
- a second comparator, having a fifth input terminal, a sixth input terminal and a third output terminal, and wherein the sixth input terminal of the second comparator is coupled to a second reference voltage;
- a first resistor, coupled between the fifth input terminal of the second comparator and the third output terminal of the second comparator; and
- a second resistor, having one terminal coupled to the fifth input terminal of the second comparator and another terminal coupled to at least one control signal.
20. The PWM apparatus of claim 19, further comprising a first rectifying device coupled between the third output terminal of the second comparator and the third input terminal of the first comparator.
21. The PWM apparatus of claim 20, wherein the dimming signal is coupled to the second input terminal of the error signal generator through a second rectifying device.
22. The PWM apparatus of claim 18, wherein the auxiliary signal is coupled to the first output terminal of the error signal generator through a passive device.
23. The PWM apparatus of claim 22, wherein the passive device comprises a resistor or a rectifying device.
24. A control circuit suitable for controlling a pulse width modulation (PWM) apparatus, the PWM apparatus comprising an error signal generator and a feedback compensation unit, a first input terminal of the error signal generator coupled to a first reference voltage, a second input terminal coupled to a feedback signal and a first output terminal outputs an error state signal, wherein the feedback compensation unit is coupled between the second input terminal and the first output terminal, the control circuit comprising:
- a signal generator, coupled to a terminal of the feedback compensation unit for generating a signal to adjust a voltage across the feedback compensation unit.
25. The control circuit of the claim 24, further comprising a switching control unit, coupled to at least one control signal and controlling the signal generator whether or not to output the signal accordingly.
26. The control circuit of claim 25, wherein the least one control signal comprises an enable control signal, a working voltage detection signal, an error detection signal, a dimming signal, the feedback signal or the error state signal.
27. The control circuit of claim 25, wherein the terminal of the feedback compensation unit is coupled to the first output terminal of the error signal generator.
28. The control circuit of claim 27, wherein the PWM apparatus further comprises a first comparator having a third input terminal, a fourth input terminal and a second output terminal, the third input terminal receives the error state signal, the fourth input terminal receives a compare signal, and the second output terminal outputs a pulse width modulated signal.
29. The control circuit of claim 28, wherein the level of the signal of the signal generator is determined by the level of the compare signal.
30. The control circuit of claim 29, wherein the compare signal is a triangular wave or a saw-tooth wave, and the level of the signal of the signal generator is substantially equal to or below a trough level of the compare signal.
31. The control circuit of claim 25, wherein the terminal of the feedback compensation unit is coupled to the second input terminal of the error signal generator.
32. The control circuit of claim 31, wherein the level of the signal of the signal generator is determined by the first reference voltage.
33. The control circuit of claim 32, wherein the level of the second setting signal is substantially equal to or above the level of the first reference voltage.
34. The control circuit of claim 25, wherein the signal generator comprises:
- a first switch, having a first terminal, a second terminal and a first control terminal, wherein the first terminal is grounded, the second terminal is coupled to the terminal of the feedback compensation unit, and the first control terminal is coupled to the switching control unit; and
- a second switch, having a third terminal, a fourth terminal and a second control terminal, the third terminal is coupled to the terminal of the feedback compensation unit, the fourth terminal is coupled to a voltage source, and the second control terminal is coupled to the switching control unit.
35. The control circuit of claim 34, wherein the switching control unit comprises:
- an exclusive NOR gate, wherein an input terminal thereof receives an enable control signal, another input terminal thereof receives a working voltage detection signal;
- an AND gate, wherein one of input terminals thereof receives the output from the exclusive NOR gate, another input terminal thereof receives an inverted error detection signal, and the output terminal of the AND gate provides a second switching signal to the control terminal of the second switch; and
- an inverter, for receiving the second switching signal to generate a first switching signal to the control terminal of the first switch.
36. The control circuit of claim 34, wherein the switching control unit comprises:
- a first AND gate having a first input terminal, a second input terminal and an output terminal wherein the first input terminal thereof receives a working voltage detection signal of the PWM apparatus, and the second terminal thereof receives the enable control signal;
- an exclusive NOR gate, wherein an input terminal thereof receives a dimming signal, another input terminal thereof receives an output signal from the output terminal of the first AND gate;
- a second AND gate, wherein an input terminal thereof receives the signal from the output terminal of the exclusive NOR gate, another input terminal thereof receives an inverted error detection signal, and the output terminal of the second AND gate provides a second switching signal to the control terminal of the second switch; and
- an inverter, for receiving the second switching signal to generate a first switching signal to the control terminal of the first switch.
37. The control circuit of claim 25, wherein the signal generator comprises a voltage source and a switch, the voltage source is coupled to the terminal of the feedback compensation unit via the switch, and the switching control unit controls the switch so as to determine whether the voltage source provides the signal based on at least one control signal.
38. The control circuit of claim 24, wherein the signal generator comprises:
- a second comparator, having a fifth input terminal, a sixth input terminal and a third output terminal, and the sixth input terminal of the second comparator is coupled to a second reference voltage;
- a first resistor, coupled between the sixth input terminal of the second comparator and the third output terminal of the second comparator; and
- a second resistor, having a terminal coupled to the sixth input terminal of the second comparator, and another terminal coupled to at least one control signal.
39. The control circuit of claim 38, wherein the third output terminal of the second comparator is coupled to the first output terminal of the error signal generator through a passive device.
40. The control circuit of claim 39, wherein the passive device is a first rectifying device.
41. The control circuit of claim 39, wherein the least one control signal comprises a dimming signal.
42. The control circuit of claim 41, wherein the dimming signal is coupled to the second input terminal of the error signal generator through a second rectifying device.
43. A method for controlling pulse width modulation (PWM), suitable for controlling a PWM apparatus to generate a pulse width modulated signal to control a transforming circuit to drive a loading, the control method comprising the steps of:
- detecting whether or not the state of the PWM apparatus is in a specified state; and
- setting an error state signal of the PWM apparatus to a predetermined value when the state of the PWM apparatus is the specified state.
44. The method of claim 43, wherein the specified state comprises an initial state, a shut down state or an error state.
45. The method of claim 43, further comprising the steps of:
- generating the error state signal according to the operating state of the loading when the state of the PWM apparatus is not the specified state; and
- comparing the error state signal with a compare signal to generate the pulse width modulated signal, wherein the compare signal has a first level and a second level, and the first level is greater than the second level.
46. The method of claim 45, wherein the predetermined value is a voltage substantially equal to or below the second level.
Type: Application
Filed: Dec 13, 2006
Publication Date: May 29, 2008
Applicant: BEYOND INNOVATION TECHNOLOGY CO., LTD. (Taipei City)
Inventors: Li-Min Lee (Taipei City), Chung-Che Yu (Taipei City), Chih-Shun Lee (Taipei City)
Application Number: 11/609,908
International Classification: H03K 7/08 (20060101);